Members of this family are YpeB, a protein usually encoded with the putative spore-cortex-lytic enzyme SleB and required, together with SleB, for normal germination. This family is retricted to endospore-forming species in the Firmicutes lineage of bacteria, and found in all such species to date except Clostridium perfringens. The matching phenotypes of mutants in SleB (called a lytic transglycosylase) and YpeB suggests that YpeB is necessary to allow SleB to function.